. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. UNICELLULAR PLANTS. 9 and unstable. The nucleus plays a prominent part in the life- Mstory of the cell, and seems to be essential to its perfect devel- opment and greatest physiological UNICEIXULAE PLANTS. Yeast (Tonda, Saccharomyces Cerevisice). The essential part of the common substance, yeast, may be studied to advantage, as it affords a simple type of a vast group of organisms of profound interest to the student of physiology and m
. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. UNICELLULAR PLANTS. 9 and unstable. The nucleus plays a prominent part in the life- Mstory of the cell, and seems to be essential to its perfect devel- opment and greatest physiological UNICEIXULAE PLANTS. Yeast (Tonda, Saccharomyces Cerevisice). The essential part of the common substance, yeast, may be studied to advantage, as it affords a simple type of a vast group of organisms of profound interest to the student of physiology and medicine. To state, first, the main facts as ascertained by observation and experi- ment: Uorphological. — The particles of which yeast is composed are cells of a circular or oval form, of an average diameter of about -j^ of an inch. Each individual torula cell consists of a trans- parent homogeneous cov- ering (celliilose) and gran- ular semifluid contents (protoplasm). Within the latter there may be a space (vacuole) filled with more fluid contents. The various cells pro- duced bv buddinar mav ^°- S-—Tte endogomdia (ascospore) phase of repro- •' , ° , •' ductioa—i. e., endogenous division. remain united like strings of beads. Collections of masses composed of four or more subdivisions (as- cospores), which finally separate by rupture of the original cell wall, having thus become themselves inde^ pendent cells, may be seen more rarely (endogenous division). Fig. 2.—^Various stages in the development of brewer's yeast, seen, with the exception of the first in the series, with an ordlnaiy high power (Zeiss, D. 4) of the microscope. The first is greatly magnified (Gundlach''s t^ immersion lens). The second series of four represents stages in the division of a single cell; and the third series a branching colony. Everywhere the hght areas indicate Please note that these images are extracted from scanned page images that may have been digitally enhanced for
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